Typical iron club heads are solid with flat hitting faces and generally configured as either muscle back or cavity back clubs. Traditionally, all irons were configured as muscle back clubs, which are smooth at the back with low offset, a thin topline and a thin sole. Cavity back irons have a hollowed out back and the club head mass is redistributed to the sole and the perimeter of the club head, which moves the center of gravity lower to the ground and rearward. The weight distribution makes the iron launch the ball higher and increases rotational moment of inertia thereby lowering its tendency to rotate on mis-hits and enlarging the sweet spot.
Some muscle back irons have an interior hollow section, such that the club resembles a muscle back on the outside but the interior hollow section alters the club's mass characteristics. One example is U.S. Pat. No. 4,645,207 to Teramoto et al. The Teramoto patent discloses a set of iron golf clubs in which the iron club is cast by the lost wax method, and the back member is welded at the back of the face member to form a hollow section between the back and face members. As the club changes from a longer iron to a shorter iron, the hollow section is gradually decreased to zero and the sole width is gradually decreased. No support is provided to the hitting face.
Another example is U.S. Pat. No. 4,754,969 to Kobayashi. The Kobayashi patent discloses a set of golf clubs wherein each one-piece club head includes a hollow section behind the striking face. Each of the club heads is made of a stainless steel by, for example, a lost wax casting process. The material of each of the face portions of the club heads is then annealed to increase its elasticity. The striking face is thinner for long irons, but no support is provided to the hitting face.
Another example is U.S. Pat. No. 7,126,339 to Nagai et al., which discloses utility golf clubs, which generally include a hollow interior.
Previous muscle-back club heads generally have a low moment of inertia about the longitudinal axis of the shaft (“MOI-SA”) because they are relatively small. Because of their size, they also tend to have a low moment of inertia about a vertical axis extending through the center of gravity (“MOI-Y”). Conversely, previous game improvement club heads have relatively higher MOI-Y, at the expense of a higher MOI-SA because they are relatively large. Generally, better players have a tendency to prefer golf clubs having a lower MOI-SA so that they can control the orientation of the club head throughout the swing with greater ease. However, because even the better player will experience imperfect ball strikes, they are often penalized by the associated lower MOI-Y of the small club heads.
There remains a need in the art for an improved iron-type golf club. In particular, there is a need for an iron-type golf club that provides a lower MOI-SA in combination with a higher MOI-Y.